A series connection of power electrolytic capacitors is often specified in order to achieve an adequate voltage rating of a capacitor assembly. A DC link of a frequency converter can include such an assembly. By their nature, electrolytic capacitors exhibit leakage current. The leakage currents of the series-connected capacitors are most likely not equal. This creates differential leakage currents which make the voltage sharing of the capacitors non-ideal. Therefore, so-called balancing resistors can be used in parallel with the capacitors. The resistors can be adjusted to produce currents much larger than the differential currents so that the resistors dominate the voltage sharing.
However, this approach has some drawbacks. First, the resistance value must be low enough in order to ensure that the resistor current is the dominant one in the voltage sharing. This leads to considerable power dissipation, thus reducing the efficiency of the equipment. Second, the resistances in series must match each other with high accuracy. The deviations of the resistances will otherwise off-balance the voltage sharing.